We had the missing captcha problem going to 3.0.6. It was fixed, but I was never 100% sure what fixed it. I posted the support question in this topic:
http://www.phpbb.com/community/viewtopi ... &t=1869355
Here is someone who fixed theirs by refreshing the style:
http://www.phpbb.com/community/viewtopi ... &t=1999555
Here is someone who fixed theirs by purging the cache:
http://www.phpbb.com/community/viewtopi ... &t=1903915
On our board, we had both avatars and captcha missing. I read that it was probably caused by an extra space or line before or after the beginning/ending tags of a php file. So I spent hours
opening files in my file editor and looking for extra lines or spaces, finding nothing.
We had a test board and the main board, both were upgraded, both had the missing captcha. Finally on the test board I found an extra line at the end of the config file (one of the last places I looked because I knew I hadn't touched it) and that fixed the captcha on the test board. But I corrected the same thing on the main board and it did not fix it, so I kept looking. I found another file (moderator_needed.php) that had an extra line at the end, and after I fixed that the captcha appeared on the main board.
It makes no sense because moderator_needed.php had been on the server like that for 9 months and hadn't caused any problem. I am not sure fixing those 2 files is what made the captchas appear on the 2 boards, however they were fixed after I did it.
I wasted a bunch of time trying to find spaces using inadequate technique and had to look through a bunch of files again.
in an email I wrote: I thought I had checked the php files. I knew it wasn't good enough to just click View in my ftp program, so I was actually downloading them to the desktop and viewing them in my proper edit program there. Well, that still isn't enough. That will let you find any spaces before the first php tag, but it doesn't help at all to find a space after the closing tag. To do that you have to
1) open the file in a proper file editor (with line numbers)
2) scroll to the end of the file
3) use the mouse to locate the cursor on the last line of the file...but click it over in the right margin of the line. The cursor will automatically jump over to the left and focus itself on the last character...which may be a space.
This can take hours and hours, you might want to wait till you've exhausted other options.